Trauma to the brain of man often leads to irreversible damage by a severing of nerve fibers which cannot regrow. Unlike man, organisms such as fish are able to regenerate central nervous tissue. Transection of the optic tract in the goldfish initiates a remarkable growth process during which axons of retinal ganglion cells grow back into the optic tectum with the formation of new synpases and the recovery of sight. During this regeneration, glia of the optic tract show marked increases in new protein biosynthesis and cellular proliferation. I propose a Target Regulation Hypothesis which suggests that these glia are stimulated in part by an association with regenerating axons and in part by the release of humoral factors from the synaptic target site. "Activated" glia may then play an important role in regulating the patterns of early axonal growth. I will use biochemical and morphological markers in order to characterize the signals which activate glia and to investigate what influence such activated glia may have upon regenerating neurons. Six different surgical preparations will be employed in an effort to uncover putative neuronal or target tissue influences upon glia of the optic tract. The biologic response of specific glial cell populations will be monitored by cell counts using immuno-histochemical markers, by quantitating incorporation of radiolabelled precursors using electron microscopic autoradiography, by measuring the activity of the myelin membrane enzyme 2 feet:3 feet-cyclic nucleotide 3 feet-phosphohydrolase, and by analyzing specific biosynthetically labelled proteins using socium dodecyl sulphate polyacrylamide gel electrophoresis. Application of these techniques to tissues recovered from the various surgical preparations will allow identification of growth regulating factors which stimulate glia in vivo. Conventional biochemical methods will next be used to isolate soluble and membrane associated factors that stimulate glia in vitro. In this way I hope to further our understanding of the molecular basis for neuronal regeneration.